NICEClassif | R Documentation |
NICE (Brughmans and Martens 2021) searches for counterfactuals by iteratively replacing feature values
of x_interest
with the corresponding value of its most similar (optionally correctly classified) instance x_nn
.
NICE starts the counterfactual search for x_interest
by finding its most similar (optionally) correctly classified
neighbor x_nn
.
In the first iteration, NICE creates new instances by replacing a different feature value of x_interest
with the corresponding
value of x_nn
in each new instance. Thus, if x_nn
differs from x_interest
in d
features, d
new instances are created.
Then, the reward values for the created instances are computed with the chosen reward function.
Available reward functions are sparsity
, proximity
, and plausibility
.
In the second iteration, NICE creates d-1
new instances by replacing a different feature value of the highest
reward instance of the previous iteration with the corresponding value of x_interest
, and so on.
If finish_early = TRUE
, the algorithm terminates when the predicted desired_class
probability for
the highest reward instance is in the interval desired_prob
; if finish_early = FALSE
, the
algorithm continues until x_nn
is recreated.
Once the algorithm terminated, it depends on return_multiple
which instances
are returned as counterfactuals: if return_multiple = FALSE
, then only the highest reward instance in the
last iteration is returned as counterfactual; if return_multiple = TRUE
, then all instances (of all iterations)
whose predicted desired_class
probability is in the interval desired_prob
are returned as counterfactuals.
If finish_early = FALSE
and return_multiple = FALSE
, then x_nn
is returned as single counterfactual.
This NICE implementation corresponds to the original version of Brughmans and Martens (2021) when
return_multiple = FALSE
, finish_early = TRUE
, and x_nn_correct = TRUE
.
counterfactuals::CounterfactualMethod
-> counterfactuals::CounterfactualMethodClassif
-> NICEClassif
x_nn
(logical(1)
)
The most similar (optionally) correctly classified instance of x_interest
.
archive
(list()
)
A list that stores the history of the algorithm run. For each algorithm iteration, it has one element containing
a data.table
, which stores all created instances of this iteration together with their
reward values and their predictions.
new()
Create a new NICEClassif object.
NICEClassif$new( predictor, optimization = "sparsity", x_nn_correct = TRUE, return_multiple = FALSE, finish_early = TRUE, distance_function = "gower" )
predictor
(Predictor)
The object (created with iml::Predictor$new()
) holding the machine learning model and the data.
optimization
(character(1)
)
The reward function to optimize. Can be sparsity
(default), proximity
or plausibility
.
x_nn_correct
(logical(1)
)
Should only correctly classified data points in predictor$data$X
be considered for the most similar instance search?
Default is TRUE
.
return_multiple
(logical(1)
)
Should multiple counterfactuals be returned? If TRUE, the algorithm returns all created instances whose desired_class
prediction is in the interval desired_prob
. For more information, see the Details
section.
finish_early
(logical(1)
)
Should the algorithm terminate after an iteration in which the desired_class
prediction for the highest reward instance
is in the interval desired_prob
. If FALSE
, the algorithm continues until x_nn
is recreated.
distance_function
(function()
| 'gower'
| 'gower_c'
)
The distance function used to compute the distances between x_interest
and the training data points for finding x_nn
. If optimization
is set
to proximity
, the distance function is also used for calculating the
distance between candidates and x_interest
.
Either the name of an already implemented distance function
('gower' or 'gower_c') or a function is allowed as input.
If set to 'gower' (default), then Gower's distance (Gower 1971) is used;
if set to 'gower_c', a C-based more efficient version of Gower's distance is used.
A function must have three arguments x
, y
, and data
and should
return a double
matrix with nrow(x)
rows and maximum nrow(y)
columns.
clone()
The objects of this class are cloneable with this method.
NICEClassif$clone(deep = FALSE)
deep
Whether to make a deep clone.
Brughmans, D., & Martens, D. (2021). NICE: An Algorithm for Nearest Instance Counterfactual Explanations. arXiv 2104.07411 v2.
Gower, J. C. (1971), "A general coefficient of similarity and some of its properties". Biometrics, 27, 623–637.
if (require("randomForest")) {
# Train a model
rf = randomForest(Species ~ ., data = iris)
# Create a predictor object
predictor = iml::Predictor$new(rf, type = "prob")
# Find counterfactuals
nice_classif = NICEClassif$new(predictor)
cfactuals = nice_classif$find_counterfactuals(
x_interest = iris[150L, ], desired_class = "versicolor", desired_prob = c(0.5, 1)
)
# Print the results
cfactuals$data
# Print archive
nice_classif$archive
}
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